The instant invention relates to a fused refractory grain and refractory mixes and shapes made therefrom, particularly to magnesite-spinel brick.
With the phasing out of chrome-containing brick due to the toxicity problems inherent with hexavalent chromium compounds, efforts to replace the same have included magnesite-spinel brick.
Magnesite-spinel brick and other refractory shapes made from magnesite-spinel refractory mixes are in wide usage, and while generally satisfactory they have relatively low strength of about 100 to 300 psi at high temperatures, i.e., at about 2500.degree. and above.
The low strength arises due to eutectic melting which occurs when lime and, to a lesser extent, silica within the magnesite portion of the spinel grain react with the alumina component of the spinel grain.
Efforts to increase the high temperature strengths have not been successful despite the addition of various additives.